Make mkdocs serve/build --strict optional, move locales dir.

[kattni]

This makes the --strict flag on serve and build configurable to provide the option to build with errors. To use:

tox -e docs-live -- --build-with-errors

Or:

tox -e docs-all -- --build-with-errors

It also moves the locales directory into the docs directory to avoid a full redo of the Weblate configuration on the Tutorial.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

I've added some content change to verify that the post-merge translation workflow works - I noticed that this PR includes PO updates, which (generally speaking) shouldn't be required; and then saw that the translation workflow hard-coded the docs/locales path and was failing. This change should make that workflow work again.

[freakboy3742]

And confirmed that (once I gave Brutus permissions), the translation update workflow worked, yielding this update